A problem of color distortion can arise in color television receivers of the type having both RF (radio frequency) and baseband video input signal sources. More specifically, when one displaying a video signal provided from an RF signal source provided by a tuner and associated IF (intermediate frequency) amplifier and detector, it is necessary to filter the chrominance signal to correct for sideband distortion. Distortion results because the IF filter tends to suppress the upper sideband of the chrominance signal relative to the lower sideband and this unbalance of sidebands can lead to visible color distortion in displayed images. Conventionally, the correction is made by use of a chrominance band pass filter having a "sloped" or non-symmetrical response which attenuates the lower sideband such that the overall response is about the same (symmetrical) for the two sidebands. On the other hand, video signals provided by an auxiliary baseband video input are typically reasonably well balanced (symmetrical) signals and require only conventional symmetrical band pass filtering.
Color television receivers with source dependent variable chrominance signal filtering are known. An example is described by Sendelweck et al. in U.S. Pat. No. 5,107,341 entitled COLOR TELEVISION APPARATUS WITH PICTURE IN PICTURE PROCESSING AND WITH VARIABLE CHROMINANCE SIGNAL FILTERING which issued Apr. 21, 1992. An exemplary embodiment of the Sendelweck receiver includes a picture-in-picture processor and a variable filtering circuit for switching between a "slope" type filter and a symmetrical or "haystack" type of filter. A control signal is supplied to the filter selection switch so as to select the "slope" type filter for the chrominance signal when the main picture being displayed is provided by an RF signal source and for selecting the "haystack" or symmetrical filter when the main picture being displayed is provided from an auxiliary video source.